Synthetic resins, including polypropylene, polycarbonate, polystrene, polyesters and aliphatic polyamides, such as nylon-6,6 and nylon-6, and copolymers and blends thereof, are often used for molded articles and fibers. In many uses, particularly for molded articles, it is preferred that the resin have improved resistance to fire, compared to the resin alone. This is often attained by the addition of various agents which improve the basic fire resistance of the resin, but sometimes these agents degrade or diminish other physical properties of the resin. Since resins are widely used, compositions which have improved fire resistance but yet retain the desirable physical properties of the resin are constantly being sought.
German Patents 2,150,484 and 2,130,793, and A. E. Lipska, Comb. Inst. Arizona State Univ., West. State Sect. Combust. Inst. WSCI, 1973, report that certain tungsten compounds can be used in various ways to improve the fire resistance of polyamides. The combinations of agents described hereinafter are not disclosed in these references.
U.S. Pat. No. 4,298,518 discloses compositions containing polyamides and melamine cyanurate, which are said to have good fire resistance.
U.S. Pat. No. 3,458,470 discloses compositions containing polyamides and a variety of tungsten or molybdenum compounds, including silico- and phosphotungstic acids. These compositions are said to have good resistance to discoloration and be stable to light. U.S. Pat. No. 3,936,416 discloses that polystyrene (PS), polypropylene (PP), and polyethylene (PE) are flame proofed by combination of melamine pyrophosphate (MPP) and dipentaerythritol, but requires about a 45% loading of the total resin plus flame retardant composition.
Melamine phosphate may be added to synthetic resins to improve the flame retardancy of the resins, but when heated to normal engineering polymer processing temperatures the melamine phosphate gives off so much water that the resultant mixture of the resin and the melamine phosphate has very poor physical properties.
What are needed, therefore, are flame retardant resin compositions which do not have the problems and deficiencies of the prior art, and particularly compositions with mechanical properties that are not reduced too much by the addition of flame retardants.